Conventional hacksaws have a rigid metal frame member, a handle member secured to a rear end of the frame member, and a blade tensioning device located below the handle member. One end of a serrated cutting blade is removably mounted to a forward end portion of the frame member and the other end is removably mounted to a blade tensioning device carried on or adjacent the handle member. Often the blade tensioning device is a wing nut that the user turns to tension the blade. In some arrangements the tensioning device is a pivotally mounted lever which the user pivots upwardly to tension the blade.
One problem with such conventional arrangements is that the entire metal frame member is exposed to moisture that can cause corrosion. Also, the frame member may become damaged or chipped when dropped or otherwise impacted against a hard surface. Conversely, the hard metal of the frame may damage certain surfaces, such as finished surfaces, when dropped thereon. A solution to this problem is to overmold the metal frame member with plastic material. The plastic material protects the frame member from corrosion and from direct impacts. This concept is shown in U.S. Pat. No. 5,673,488 to Grayo.
Simply molding plastic over the metal frame member as shown in the '488 patent does little to increase the overall strength and rigidity of the hacksaw frame member, however. The metal frame member still provides the hacksaw with almost all of its structural rigidity. The plastic just protects the metal member and improves the aesthetics of the hacksaw and provides a negligible amount of rigidity, if any. As a result, the metal frame member in the '488 patent must be made relatively thick to provide sufficient rigidity. However, this increases the overall cost and weight of the hacksaw.
It is therefore an object of the present invention to provide a hacksaw with a plastic/metal composite frame in which the plastic is specially configured to substantially contribute the frame's structural rigidity so that a lighter metal frame member can be used. To achieve this object, one aspect of the present invention provides a hacksaw comprising an elongated blade having opposing longitudinal end portions and a cutting edge between the longitudinal end portions and an over molded frame assembly in which the blade is mounted. The overmolded frame assembly includes a rigid metal frame member having a longitudinal portion thereof covered in surrounding relation by solidified plastic material. The solidified plastic material has an I-beam configuration with upper and lower end caps on opposing sides thereof extending longitudinally with respect to the frame member and a generally vertical web extending between the upper and lower end caps.
A first blade mounting structure is carried by the hacksaw and one of the longitudinal end portions of the blade being removably mounted on the first blade mounting structure. A releasable blade tensioning device is carried by the hacksaw and provides a second blade mounting structure. The other of the longitudinal end portions of the blade is removably mounted on the second blade mounting structure and the blade tensioning device is constructed and arranged to affect relative movement between the first and second blade mounting structures to tension the blade in the longitudinal direction thereof and thereby apply a rearwardly directed force to a forward end portion of the metal frame member. The blade tensioning device is also constructed and arranged to affect relative movement between the first and second blade mounting structures to release the tension and allow for removal and replacement of the blade. The rearwardly directed force applied to the forward end portion of the frame member creates a bending moment in the frame assembly which the metal frame member and the solidified plastic material with an I-beam configuration cooperate to resist. The hacksaw further includes a manually engageable handle member that can be manually grasped to enable performance of a cutting operation wherein the cutting edge of the tensional blade is engaged with a workpiece and moved forwardly and rearwardly to cut the workpiece.
The I-beam shape of the solidified, plastic material is particularly desirable because the upper and lower end caps are located at the points where the tensile forces are the highest in the frame member when a bending force is applied by the blade. Specifically, using the I-beam configuration provides the desired protection of the metal frame and also enhances the frame's overall structural rigidity. Thus, a lighter metal member can be used without sacrificing the durability and rigidity of the frame.
In one preferred embodiment of the hacksaw the handle member is molded integrally with the frame assembly from the solidified plastic material so as to define an overmolded handle and frame assembly.
It should be noted that, in accordance with this aspect of the invention, the molded plastic does not have to conceal the entire frame member. In fact, it is contemplated to leave small "windows" in the plastic material through which the metal of the frame member is visibly exposed. This allows the consumer to visibly confirm that a metal frame member is being used in the hacksaw's construction, which gives the impression of added ruggedness and durability that may not be conveyed by a construction wherein the frame member 22 is completely concealed and the consumer can only see a plastic exterior.
A related aspect of the present invention provides a method for making a hacksaw. The method of this aspect of the invention comprises providing a rigid metal frame member, overmolding molten plastic material in surrounding relation over a longitudinal portion of the frame member and solidifying the molten plastic material so as to provide the plastic material with an I-beam configuration having upper and lower end caps on opposing sides thereof extending longitudinally with respect to the frame member and a generally vertical web extending between the end caps. The manually engageable handle member is provided rearwardly of the metal frame member either before, during or after the overmolding and solidifying of the plastic material such that the metal frame member, the plastic material supporting the metal frame member and the handle member define the handle and frame assembly. The handle of the frame assembly provides a first blade mounting structure. The next step comprises mounting a releasable blade tensioning device with a second blade mounting structure to the handle and frame assembly. Opposing longitudinal end portions of an elongated blade are removably mounted to the first and second mounting structures. The blade has a cutting edge that extends generally between its longitudinal end portions. The tensioning device is constructed and arranged to affect relative movement between the first and second blade mounting structures to thereby tension the blade between the first and second blade mounting structures. The tensioned blade applies a rearwardly directed force to a forward end portion of the metal frame member so as to create a bending moment in both the metal frame member and the solidified plastic material with an I-beam configuration. The frame member and the plastic material cooperate to resist the bending movement created by the rearwardly directed force.
As mentioned above, conventional hacksaws often use threaded wing nuts to tension the blade. However, the proper amount of tension for hacksaw blades is relatively high and over time this tension can cause the threads on the wing nut to wear down. As a result of these threads wearing down, proper blade tension can be difficult to achieve because the worn down threads may permit jiggle or play of the wing nut. To this end, there have been provided blade tensioning devices that use pivoting levers to apply the required blade tension. For example, U.S. Pat. No. 5,826,344 to Phelon et al. discloses a hacksaw in which a lever is pivotally mounted on a pivot pin and a cam is used to move the lever between tensioning and releasing positions. The entire tension load applied by the blade, however, is borne by the pivot pin. As a result, either a more robust pivot pin must be used or else the pin will fatigue over time and hence cause failure of the tensioning device.
To overcome this problem, it is therefore an object of the present invention to provide a hacksaw having a tensioning device wherein the structure that mounts the device does not bear the full tension load of the blade. To achieve this object, another aspect of the present invention provides a hacksaw wherein the handle and frame assembly provides a generally rearwardly facing load bearing surface and wherein the tensioning device provides a load transmitting surface that is engageable with the load bearing surface. The mounting structure is spaced apart from the load bearing surface and movably mounts the blade tensioning device to the handle and frame assembly.
The tensioning device is constructed and arranged to be moved between (1) a blade tensioning position wherein the first and second blade mounting structures are moved relative to one another so as to tension the blade and thereby apply a generally forwardly directed force to the blade tensioning device and a rearwardly directed force to the forward end portion of the frame member and (2) a blade releasing position wherein the first and second blade mounting structures are moved relative to one another so as to release the tension from the blade and thereby allow removal and replacement of the blade. In the blade tensioning position, the load transmitting surface engages the load bearing surface so that at least a portion of the generally forwardly directed force applied to the tensioning device is transmitted to and borne by the load bearing surface, thereby preventing the entire forwardly directed force from being borne by the mounting structure.
Preferably the load bearing surface has an arcuate, convex configuration and the load transmitting surface has an arcuate, concave configuration and the load bearing surface is spaced generally forwardly from the mounting structure.
A further aspect of the present invention relates to the manner in which the metal hacksaw frame members are formed. Typically, metal frame members are stamped or otherwise cut from sheet metal blanks. Much of the sheet metal in these blanks is trimmed off when the members are form and is discarded as scrap. It is desirable to provide a method wherein the amount of scrap produced during the fabrication of the frame members is substantially reduced or eliminated.
It is therefore yet another object of the present invention to meet this desire. Yet another aspect of the present invention achieves this further object by providing a method of forming the frame member by disposing a sheet metal blank in a stamping die assembly, engaging a stamping die with the blank so as to separate a plurality of frame members with opposing first and second longitudinally extending edges from the blank, and then selecting the frame member from plurality of frame members. The stamping die engages the blank in such a manner that (1) the first edge of each frame member is sheared from and is substantially congruent with the second edge of a frame member which is immediately adjacent the first edge and (2) the second edge of each frame member is sheared from and is substantially congruent with the first edge of a frame member which is immediately adjacent the second edge.
Preferably the stamping die provides the first and second edges of each frame member with arcuate shapes and preferably the arcuate shape of the first edge of each frame member is defined along a portion of a first imaginary circle and the second edge of each frame member is defined along a portion of a second imaginary circle. The first and second imaginary circles having the equal radii and spaced apart centerpoints.
It can be appreciated that no metal needs to be trimmed from the longitudinal edges of the frame members stamped in accordance with the principles of the present invention. Specifically, because their first and second edges are congruent, no excess material is left therebetween. Of course, some filing and grinding operations may be performed to smooth out the edges after the stamping operation; but otherwise there is no need to trim material from the longitudinal edges.
Other objects, features, and advantages of the present invention will become apparent from the following detailed description, the accompanying drawings, and the appended claims.